Deneb Vega Lite Map not displaying

Hi,

I am using the deneb visualisation and I am trying to create a map of Australia, there aren't any errors coming up with the below json code but my map is not displaying. Does anyone know what I am doing wrong?

{
  "$schema": "https://vega.github.io/schema/vega-lite/v5.json",
  "width": 500,
  "height": 300,
  "layer": [
    {
      "data": {
        "url": "https://raw.githubusercontent.com/alwaysblazing/Australia-State-TopoJson-MapChart/master/au-states-topo.json",
        "format": {
          "type": "topojson"
          }
      },
      "projection": {
        "type": "mercator"
      },
      "mark": {
        "type": "geoshape",
        "fill": "lightgray",
        "stroke": "white"
      }
    },
    {
      "data": {
        "url": "Electorate"
      },
      "projection": {
        "type": "mercator"
      },
      "mark": "circle",
      "encoding": {
        "longitude": {
          "field": "Long",
          "type": "quantitative"
        },
        "latitude": {
          "field": "Lat",
          "type": "quantitative"
        },
        "size": {"value": 10},
        "color": {"value": "steelblue"}
      }
    }
  ]

This is the data I am using Australian Post Codes - Matthew Proctor

Any help would be appreciated.

Cheers,

Chris